Module 1 Introduction 1 What is an operating

Module 1: Introduction 1 What is an operating system? Simple Batch Systems Multiprogramming Batched Systems Time-Sharing Systems Personal-Computer Systems Parallel Systems Distributed Systems Real -Time Systems Operating System Concepts M. Rathi, AP(SG)

What is an Operating System? 2 A program that acts as an intermediary between a user of a computer and the computer hardware. Operating system goals: Execute user programs and make solving user problems easier. Make the computer system convenient to use. Use the computer hardware in an efficient manner. Operating System Concepts M. Rathi, AP(SG)

Computer System Components 3 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers). Operating System Concepts M. Rathi, AP(SG)

4 Abstract View of System Components Operating System Concepts

Operating System Definitions 5 Resource allocator – manages and allocates resources. Control program – controls the execution of user programs and operations of I/O devices. Kernel – the one program running at all times (all else being application programs). Operating System Concepts M. Rathi, AP(SG)

Hardware Features 6 1. Mainframe Systems 1. 2. 3. 4. Desktop systems Multiprocessor Systems Distributed systems 1. 2. 5. Batch systems Multiprogrammed systems Time sharing Systems Client-Server systems Peer-to-peer systems Real-time systems Operating System Concepts M. Rathi, AP(SG)

1. Mainframe Systems 7 First computers to tackle many commercial and scientific applications 1. 1 Batch Systems Batch processing is a technique in which an Operating System collects the programs and data together in a batch before processing starts. Operating System Concepts M. Rathi, AP(SG)

Batch Processing Systems 8 An operating system does the following activities related to batch processing − The OS defines a job which has predefined sequence of commands, programs and data as a single unit. The OS keeps a number a jobs in memory and executes them without any manual information. Jobs are processed in the order of submission, i. e. , first come first served fashion. When a job completes its execution, its memory is released and the output for the job gets copied System Concepts into an output. Operating spool for later printing or M. Rathi, AP(SG)

9 Memory Layout for a Simple Batch System Operating System Concepts

Batch Processing (Contd. . ) 10 Advantages Batch processing takes much of the work of the operator to the computer. Increased performance as a new job get started as soon as the previous job is finished, without any manual intervention. Disadvantages Difficult to debug program. A job could enter an infinite loop. Due to lack of protection scheme, one batch job can affect pending jobs. Operating System Concepts M. Rathi, AP(SG)

Multiprogrammed Systems 11 • Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. • Multiprogramming assumes single shared processor. a • Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. Operating System Concepts

Multi. Programming (Contd. . ) 12 An OS does the following activities related to multiprogramming. The operating system keeps several jobs in memory at a time. This set of jobs is a subset of the jobs kept in the job pool. The operating system picks and begins to execute one of the jobs in the memory. Multiprogramming operating systems monitor the state of all active programs and system resources using memory management programs to ensures that the CPU is never idle, unless there are no jobs to process. Operating System Concepts M. Rathi, AP(SG)

13 OS Features Needed for Multiprogramming I/O routine supplied by the system. Memory management – the system must allocate the memory to several jobs. CPU scheduling – the system must choose among several jobs ready to run. Allocation of devices. Operating System Concepts M. Rathi, AP(SG)

Multi. Programming (Contd. . ) 14 Advantages High and efficient CPU utilization. User feels that many programs are allotted CPU almost simultaneously. Disadvantages CPU scheduling is required. To accommodate many jobs in memory, memory management is required. Operating System Concepts M. Rathi, AP(SG)

15 Time-Sharing Systems (Multitasking) Multitasking is when multiple jobs are executed by the CPU simultaneously by switching between them. Switches occur so frequently that the users may interact with each program while it is running. Operating System Concepts M. Rathi, AP(SG)

Time-Sharing Systems (Contd. . ) 16 An OS does the following activities related to multitasking − The user gives instructions to the operating system or to a program directly, and receives an immediate response. The OS handles multitasking in the way that it can handle multiple operations/executes multiple programs at a time. These Operating Systems were developed to provide interactive use of a computer system at a reasonable cost. A time-shared operating system uses the concept of CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared CPU. Each user has at least one separate program. M. in Operating System Concepts Rathi, AP(SG) memory.

17 Desktop (Personal-Computer) Systems Personal computers – computer system dedicated to a single user. I/O devices – keyboards, mice, display screens, small printers. User convenience and responsiveness. Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features. Operating System Concepts M. Rathi, AP(SG)

18 Multiprocessor Systems (Parallel Systems) Multiprocessor systems with more than one CPU in close communication. Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. Operating System Concepts M. Rathi, AP(SG)

Parallel Systems (Cont. ) 19 Symmetric multiprocessing (SMP) Each processor runs an identical copy of the operating system. Many processes can run at once without performance deterioration. Most modern operating systems support SMP All the processors are in a peer to peer relationship i. e. no master - slave relationship exists between them. Operating System Concepts M. Rathi, AP(SG)

20 Symmetric Multiprocessing Architecture Operating System Concepts

21 ASymmetric Multiprocessing Architecture In asymmetric systems, each processor is given a predefined task. There is a master processor that gives instruction to all the other processors. Asymmetric multiprocessor system contains a master slave relationship. Master processor schedules and allocates work to slave processors. More common in extremely large systems Operating System Concepts M. Rathi, AP(SG)

22 Advantages of Multiprocessor Systems : Increased throughput If multiple processors are working in tandem, then the throughput of the system increases Economical Multiprocessor systems are cheaper than single processor systems in the long run because they share the data storage, peripheral devices, power supplies etc. Increased reliability If one processor fails, the system will not halt. The ability to continue working despite hardware Operating System Concepts M. Rathi, AP(SG) failure - graceful degradation

23 Disadvantages of Multiprocessor Systems Increased Expense Complicated Operating System a multiprocessor system that share peripherals, memory etc. So, it is much more complicated to schedule processes and impart resources to processes than in single processor systems. Large Main Memory Required All the processors in the multiprocessor system share the memory. So a much larger pool of memory is required as compared to single processor systems. Operating System Concepts M. Rathi, AP(SG)

Distributed Systems 24 Networks are typecast based on the distances between their nodes. Local-area network (LAN) - a room, a floor, or a building. Metropolitan-area network (MAN) – Within a city. Wide-area network (WAN) - cities, or countries. Blue. Tooth - small-area network. Operating System Concepts M. Rathi, AP(SG)

Distributed Systems (Contd. . ) 25 A distributed environment refers to multiple independent CPUs or processors in a computer system. Loosely Coupled System An operating system does the following activities related to distributed environment − The OS distributes computation logics among several physical processors. The processors do not share memory or a clock. Instead, each processor has its own local memory. The OS manages the communications between the processors. They communicate with each other through various communication lines. Operating System Concepts M. Rathi, AP(SG)

26 Distributed Systems (Contd. . ) Client Server Systems Centralized systems today act as server systems to satisfy requests generated by client systems. Server systems can be broadly categorized as compute servers and file servers. Compute-server systems provide an interface to which clients can send requests to perform an action, in response to which they execute the action and send back results to the client. Operating System Concepts M. Rathi, AP(SG) File-server systems provide a file-system

27 Distributed Systems (Contd. . ) Client Server Systems Operating System Concepts M. Rathi, AP(SG)

28 Distributed Systems (Contd. . ) Peer-to-peer systems Internet and www Usage of email, ftp Operating System Concepts M. Rathi, AP(SG)

Distributed Systems 29 Advantages of distributed systems. Resources Sharing Computation speed up – load sharing Reliability Communications Operating System Concepts M. Rathi, AP(SG)

Distributed Systems (Cont. ) 30 Network Operating System provides file sharing provides communication scheme runs independently from other computers on the network Distributed Operating System less autonomy between computers gives the impression there is a single operating system controlling the network. Operating System Concepts M. Rathi, AP(SG)

Real-Time Systems 31 System that is subjected to real time, i. e. , response should be guaranteed within a specified timing constraint or system should meet the specified deadline. Used as a control device in a dedicated application For example: flight control system, real time monitors , medical imaging systems, industrial control system etc. Operating System Concepts M. Rathi, AP(SG)

Types of real time systems 32 Hard real-time system. Secondary storage limited or absent, data stored in short-term memory, or read-only memory (ROM) Conflicts with time-sharing systems, not supported by general-purpose operating systems. Soft real-time system Limited utility in industrial control or robotics Useful in applications (multimedia, virtual System Concepts M. Rathi, AP(SG) reality) requiring. Operating advanced operating-system